Hi,
I had this same problem after upgrading to macOS Sierra from Yosemite (needed to sync my Mac books & notes backup to a new PRS-T3 reader) and managed to solve it by disabling the mac firewall (and csrutil but that alone did not do the trick).
Longer story - first I tried:
- I disabled csrutil (from recovery mode) as suggested - did NOT work, reader was still disconnected
- Downloaded the same Reader for Mac version from Sony and my Mac refused to run the app - I discovered the upgrade to Sierra had reset my app installation settings and figured I need to enable third-party apps again
- Into the System Preferences menu I noticed the Firewall, checked - Reader was not added, added it as app with allowed connections (I first disabled the firewall, but it's enough to allow the app through it) - reconnected the reader to the Mac, and Voila! - it's connected and I synced successfully 🙂
Hope this helps others.
OR